Oilfield fluids (e.g., oil, gas, and water) are generally complex mixtures of aliphatic hydrocarbons, aromatics, hetero-atomic molecules, anionic and cationic salts, acids, sands, silts, clays and a vast array of other components. The nature of these fluids, combined with the severe conditions of heat, pressure, and turbulence to which they are often subjected, are contributing factors to the formation and deposition of unwanted contaminants, such as scales, salts, paraffins, corrosion, bacteria and asphaltenes in oil and/or gas production wells.
It is well known that unwanted deposits can precipitate from saturated oilfield waters in an oil or gas well leading to a restriction in the production piping and the potential plugging of the flow path including reservoir flow paths. For instance, common mineral scales such as calcium carbonate, calcium sulfate, or barium sulfate can precipitate from produced water and create blockages in flow paths, especially in production tubulars such as well tubing and flow lines. The formation and deposition of such unwanted contaminants decrease permeability of the subterranean formation, reduce well productivity, and, in some cases, may completely block the well tubing.
Treatments to remove deposits and inhibit the formation of unwanted deposits include the use of various mechanical preventative techniques such as scrapers or reamers and chemical treatment agents such as inhibitors, acids and converters. Mechanical tools typically deployed to remove deposits include wire lines and coil tubing. Such mechanical tools may further be used as a delivery means for chemical treatment agents into production tubing. These techniques are effective when the tubular is at an approximate 180° to the point of entry as gravity helps pull the treatment device into the well. In addition, there are limited restrictions on the tool if it is pulled out of the well when the tubular is at an approximate 180° to the point of entry. Wire lines and coil tubing have limited effectiveness, however, when the tubular being treated is deviated, as in a horizontal well or “S” shaped configuration. The flexibility of the wire and coil tubing make it difficult to push a long distance past a severe deviation or multiple deviations. Chemical prevention or remedial techniques can be effective if the treatment can be delivered reliably to the target location and in sufficient quantity to do its intended function.
Other methods exist for effective delivery of chemical treatment agents to unwanted deposits. For example, the technique of “downhole squeezing” is commonly used to address formation deposits, wherein a slug of the well treatment composition is injected into the annulus, using a pre-flush, squeeze, and over flush treatment before the well can be returned to normal function. This technique requires large volumes of treatment and flush fluid in horizontal wells with a large area of perforated interval. Further treatments are typically required as the chemical residual is depleted, once again requiring large volumes of flush and treatment into the well. Such treatment methods are typically inefficient in horizontal wells because it is difficult to ensure the treatment is delivered to all the intended area. The flush and chemical additive often required large pumps and holding tanks which can add significant costs to the application.
Solid chemical additives are sometimes delivered to wells in the form of a cylinder shape known in the industry as “sticks”. The sticks are either a solid version of a chemical additive or a dissolvable shell filled with liquid chemical additive. This delivery type is effective in vertical wells but in deviated wells the shape of the cylinder and typical square ends prevent the solid treatment from being placed beyond a deviation.
Solid chemical additives in the form of a slurry are used in the industry. This type of treatment is effective in vertical wells but require a flush to aid in delivery to the bottom of the well. In a deviated well such as a horizontal well or well with multiple deviations such as an “S” shaped completion, it is important that the slurry mass not be too heavy in order for the flush to be carried past the deviation. If the density of the slurry is too high, the slurry will settle just beyond the deviation.
Capillary tubing lengths are frequently installed in wells to aid in delivery of a chemical treatment. This technique is effective in its intended function but is expensive and requires specialized equipment to install. Further, capillary tubing may not be able to extend to great depths if the deviation angle is severe or the piping extends far beyond the bend.
While solid additives have been added to the well during the completion stage, this technique has only been proven to be an effective delivery method in new wells when the opportunity to spot the chemical additive is available.
Alternative treatment methods have therefore been sought for introducing well treatment agents into producing oil and/or gas wells and especially where the well tubing is deviated or contains multiple deviations.